Transcript Multiplicity of young and nearby stars: The SACY sample

Direct imaging of substellar objects
around young and nearby stars:
The SACY sample
N. Huélamo (Laeff-INTA, Spain)
H. Bouy (UC Berkeley)
C. Torres (LNA, Brazil)
C. Melo, M. Sterzik (ESO, Chile)
G. Chauvin (LAOG, France)
D. Barrado y Navascués (Laeff-INTA, Spain)
Motivation of this work
Direct images of Substellar/planetary companions
Observations are the only way to
discriminate between formation theories.
Put constraints to physical parameters:
1. Frequency of substellar objects in wide orbits
2. Characterize their atmospheres
3. Calibrate evolutionary models
Looking for star-companion systems
Companion to stars: We can assume similar distance/age
High spatial resolution
High contrast imaging
Adaptive Optics + Large telescope
What can we learn with AO imaging?
AO ima & spec
Population of BD/planets in large orbits
Characterize the atmospheres of the objects
Targets:
Late-type Field stars
~M p *sin(i)
orbital parameters
Chauvin et al. 2007
AO imaging: Where to look….
• Substellar companions are normally searched around
young ( < 100 Myr) and nearby (d < 100pc) late-type stars.
WHY? CONTRAST
Young late-type stars: The younger the substellar object, the
brighter
10 MJup @ 10 Myr
7
8
9
M primary
(Msun)
△K
(mag)
1.0
7.5
0.5
6.6
0.1
4.3
log t
Nearby stars: we can probe smaller separations
Deep surveys to detect substellar/planetary
companions
SURVEY
Number
Targets
Age
(Myr)
Distance
(pc)
Chauvin et al (2003)
3.6/Adonis
24
< 30
≤ 50
Masciadri et al. (2005)
NACO/VLT
30
12-200
4-77
Biller et al. (2006)
NACO/VLT + SDI
45
≤ 250
≤ 50
Kasper et al. (2007)
NACO/VLT L-band
22
≤ 30
≤ 10 - 60
Lafreniere et al. (2007)
Gemini+Altair
85
30 - 5000
≤ 35
And more to come…
Confirmed substellar companions
Chauvin et al. 2007
Confirmed Substellar companions
• Most of the substellar companions to stars detected so far have
been found at separations between 100-1000 AU.
AB Pic
~100 AU
~ 260 AU
DH Tau
~ 330 AU
HD3651
~475 AU
HN Peg
Neuhauser et al. 2004
Itoh et al. 2005
Chauvin et al. 2005
Burgasser et al. 2005
Luhman et al. 2007
~795 AU
● 1 planetary-mass companion (substellar binary): sep~60 AU Chauvin et al. 2005
● No planets (or BDs) detected at very small separations
No >2 Mjup at sep. 45-200 AU
No >4 Mjup at sep. 20-40 AU
No >5 Mjup at sep > 15 AU
Lafreniere et al. 2007
Kasper et al. 2007
Biller et al. 2006
Masciadri et al. 2005
What is SACY?
What is the connection with
substellar/planetary searches?
The SACY survey
• Search for Associations Containing Young stars
Torres et al, 2003, Torres et al. 2006
-
Started by Torres et al. in 2000 after the discovery of Tucana &
Horologium d ~30 pc, age~30 Myr
(Torres et al. 2000, Zuckerman & Webb 2000)
Moving groups of Post- T Tauri stars: How to identify them?
T Tauri Stars (Age ~1 Myr)
Near-IR excess (disks)
Forbidden lines (accretion)
X-ray emission,
Lithium, etc…
-
Post-T Tauri stars (10-100Myr)
X-ray emission can persist..
Lithium
Aim: Search for young and nearby stars as optical counterparts to Xray (ROSAT) detections
The SACY project
•
Southern ROSAT Sources
 9574
•
SACY [Hip + TYC & (B-V)0.6]
 1953
•
Observed objects (not sources)
 1750
•
Data from literature
 150
G0 and later…
}
Li abundance
Radial and Rot. velocity
Lithium -- age estimation
Dynamical properties + Convergence method:
NEW MOVING GROUPS
NEW MEMBERS of known assoc.
Torres et al. have identified at least 14 young associations in the SACY
database (there are five more possible associations to confirm…) .
Torres et al. 2006; Torres et al. 2007
Prime targets for AO surveys to detect subs./planet. companions
Our study
1.
VLT/NACO survey : Substellar/Planetary
companions around new young nearby stars
identified in the SACY survey
2.
Characterization of nearby (young?) M-type
stars in the SACY Catalog that do not belong
to any moving group.
1. Search for substellar companions
around SACY stars
AO survey started on 2006
The sample of 78 targets contains:
• I.
18 New identified members of 9 young and nearby loose
associations included in Torres et al. 2007 (e.g. TW Hya, Beta Pic,
Tuc-Hor)
• II. 30 New identified members in other nearby assocs. (e.g. LCC)
• III. 15 M-type stars without lithium and/or association but probably
young…
• IV. 15 Young stars (with lithium) without association
Average properties…
• Most of them are M,K-type stars
• Ages ~ 10 Myr
• Hipparcos and/or UCAC2 Proper motions:
(Confirm companions in 1-2 yrs)
Observations
•
•
•
•
•
•
NACO/VLT
Optical WFS + IB2.27 filter
S27 objective : 27’’ x 27’’ FOV
Typical integrations of 12-15 minutes
Classical AO imaging
Service Observations (April-Sep. 2006)
Detection limits
30
60
90
120
300 (AU) @ 60pc
Δmag ~ [email protected]”
10MJup
Average curve for IB 2.27
M* = 0.8 Msun,
10 Myr
I: Nearby loose associations
Number
4
11
3
Assoc.
Age
Distance
Є Cha
6
100
β Pic
10
60
Tuc-Hor
30
30
Results
•
•
•
•
67 detected sources around 12 stars
All of them around BPA and ECA members
14 sources at separation < 5”
2 new subarsecond stellar binaries
Results
Results
Targets at separations < 500 AU from host star:
4 in ECA
13 in BPA
The most interesting substellar candidates
I. ε Cha
Sep=3.8”@103pc= 391AU
Target:
K0 star from Є Cha
d=103 pc
Age=6 Myr
Sep=0.13” @103 = 13.4 AU
10 MJup
20 MJup
Galactic latitude ~ -8 deg
The most interesting substellar candidates
I. ε Cha
Sep=1.8”@103pc= 185 AU
Target:
G8 star from Є Cha
d=115 pc
Age=6 Myr
Companion Candidate:
Sep = 210 AU
Mass < 10 MJup
Galactic latitude ~ -8 deg
The most interesting substellar candidates
II. BPA
Sep=3.9”@54pc= 210 AU
Target:
M1 star from β Pic
d= 54 pc
Age=10 Myr
3.9”
Companion Candidate:
Sep = 210 AU
Mass < 10 MJup
Galactic Latitude ~ -23 deg
The most interesting substellar candidates
II. BPA
Sep=1.7”@72 pc= 126 AU
Target:
M1 star from β Pic
d= 72 pc
Age=10 Myr
Galactic Latitude ~ -07 deg
1.7”
Companion Candidate:
Sep = 126 AU
Mass ~10 MJup
II: Lower Centaurus Crux (LCC)
• 11 new identified members
• Distances: 73-110pc
• Age ~ 8 Myr
(Torres et al., in prep.)
Substellar comp. candidates in LCC
Results:
130 detected sources
25 at separations < 5”
4
new subarc. binaries
Galactic latitudes (~ 0–8 deg)
Substellar comp. candidates in LCC
40 MJup @300 AU
15 MJup @260 AU
Gal. Latitudes: ~02 deg
Subsamples I and II:
Nature of the companion candidates?
• Wider companions (sep > 10 arcsec): BACKGROUND
cross-correlation with optical, near-IR catalogs
• Closer companions (sep < 10 arcsec)
Second epoch observations are needed… hopefully
next semester
III: M-type stars from SACY
• Our SACY sample contains 15 M-stars (M0-M3):
-
With X-ray emission
Without lithium
Do not converge to any moving group
8 (out of 15) with Hipparcos parallaxes: d ~(14-59 pc)
What is the nature of these stars?
Are they young or old?
M-type stars from SACY
• Lithium cannot be used as an age estimator since it is
depleted too fast.
β Pic – 10 Myr
…but gives as a lower limit
AB Dor – 70 Myr
age ≥ 10Myr
M-stars: Age diagnostics?
- Comparison with Evol. Tracks
- Stellar activity
- Surface gravity
M-type stars from SACY
• Comparison with evolutionary tracks
Song et al. 2003
M-type stars from SACY
• Lx / Lbol as age diagnostic
Song et al. 2003
M-type stars from SACY
• Surface Gravity can be used as an age indicator.
M⓪
M-type stars from SACY
• Gravity sensitive lines:
(e.g. Na I 5900 Å, KI D 7700 Å, Na I D 8200 Å)
• Method:
- EW measurement of alkali lines
- Comparison with templates:
Younger and older stars with similar spectral types
(on-going …)
Substellar companion candidates to M-stars?
8.6” companion
to a M1 star
He I lines
Sep. ~ 500 AU @ 59pc
Mass ~ 20 MJup @ 70 Myr
Public Archives: the system is a common proper
motion pair (obs from 1910 to 2006).
BUT
Colors not consistent with a Brown Dwarf
but with a White Dwarf.
A DB white dwarf ‘companion’ to a nearby star
Conclusions
SACY Catalog contains prime targets for AO surveys to look for substellar
and planetary-mass companions: young and nearby
Preliminary results from our NACO/VLT survey:
• 17 good substellar/planetary companion candidates to nearby stars in
nearby associations.
• Several candidates around LCC stars but …at very low galactic latitudes
(probably background…)
• Second epoch observations necessary…
Increase the number of SACY young,nearby M-stars without association
via optical, X-ray data (surface gravity, magnetic activity, etc..)